Added documentation for the rpi_pfio platform. (#2597)

* Added documentation for the rpi_pfio platform.

* Changed version to next release

* Removed unused pull mode

source/_components/binary_sensor.rpi_pfio.markdown

@@ -0,0 +1,39 @@
+---
+layout: page
+title: "PiFace Digital I/O Binary Sensor"
+description: "Instructions how to integrate the PiFace Digital I/O module into Home Assistant as a binary sensor."
+date: 2016-05-08 15:00
+sidebar: true
+comments: false
+sharing: true
+footer: true
+logo: raspberry-pi.png
+ha_category: Binary Sensor
+ha_release: 0.45
+---
+
+The `rpi_pfio` binary sensor platform allows you to read sensor values of the [PiFace Digital I/O](https://www.element14.com/community/docs/DOC-69001) .
+
+To use your PiFace Digital I/O module in your installation, add the following to your `configuration.yaml` file:
+
+```yaml
+# Example configuration.yaml entry
+binary_sensor:
+  - platform: rpi_pfio
+    ports:
+      0:
+        name: PIR Office
+        invert_logic: true
+      1:
+        name: Doorbell
+        settle_time: 50
+```
+
+Configuration variables:
+
+- **ports** array (*Required*): Array of used ports.
+  - **num** (*Required*): Port number.
+    - **name** (*Required*): Port name.
+    - **settle_time** (*Optional*): The time in milliseconds for port debouncing. Default is 20ms.
+    - **invert_logic** (*Optional*): If true, inverts the output logic to ACTIVE LOW. Default is false (ACTIVE HIGH).
+